JPH0344599B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a slurry of solid fuel in the form of pulverized carbonaceous material.

The term "solid fuel" as used in the context of the present invention refers to various types of carbonaceous materials, such as bituminous, anthracite, subbituminous and lignite, charcoal, and refinery coke, asphaltenes. Consists of solid by-products, etc.

Heat production today relies heavily on the combustion of liquid or gaseous fuels, and existing plants are therefore configured to transport, store, and burn these fuels in their natural form. Since conversion to lump coal involves extensive modification and new investment, it is not surprising that various methods of converting coal into liquid or gaseous fuel products are of great interest. In addition to the chemical conversion of coal to methanol or hydrocarbons, it has also been proposed to use some kind of liquid, such as methanol, oil, a mixture of water and oil, or just water, to produce a coal powder slurry. This allows solid fuels such as coal to be processed and transported as liquids while reducing or eliminating the amount of liquid fuels such as oil used in slurry fuels.

In many cases, a slurry of coal and water offers the most practical and economic advantages. There are many demands on solid fuel slurries, but the most important ones are that the slurry should have a high solid fuel content while also having convenient handling properties, i.e. low apparent viscosity even during long storage periods. It is to show homogeneity. Several slurry fuel production processes have already been proposed.

US Pat. No. 4,282,006 discloses a method for preparing a coal water slurry. There, the crushed coal is ground in a ball mill, and a small amount of the ground coal is further ground in another ball mill to provide a sufficient amount of fine particles for compressed pulverized coal to be used in the slurry;
This meets that requirement. This process is not completely continuous and is characterized by the first mill producing particles as large as or smaller than the largest particles in the slurry. Therefore, the resulting particle size distribution is highly dependent on the method of coal crushing in the first mill, and there is little flexibility in achieving the desired particle size distribution.

Occidental in Irvine, California
The Research Corporation published a paper (“Preparation, Handling and Combustion Properties of Coal-Water Mixtures”)
Technology '82, 5th International Coal Utilization Exhibition and Conference, December 7-9, 1982, Hyuston, Texas), in which he discloses a slurry production method. This includes a first dry milling step that produces particles within the final slurry particle size range, and a second dry milling step that further mills a portion of the first mill product to produce a sufficient amount of fine particles. Includes a pulverization process. This grinding method has the same type of drawbacks as disclosed in US Pat. No. 4,282,006.

Additionally, a method for making a coal-water slurry has been disclosed by Atlantic Research Corporation of Alexandria, Virginia (Electric Power Research Institute Report CS-2287, March 1982).
There, the coal feed is split into two before being milled. Stream 1 passes through two mills, a dry hammer mill and then a wet ball mill, with no intermediate classification. The other stream is milled in a dry cage mill in a self-contained operation. The solids produced in both streams are combined into a slurry. This operation also produces particles within the final slurry particle size range in two parallel streams and is not flexible enough to achieve the desired particle size distribution in the slurry.

Regarding particle size distribution in aqueous or non-aqueous slurries, it is well known that the particle size distribution of particle agglomeration can be optimized to minimize the viscosity of the particle agglomerated suspension at a given solids concentration. It is a fact that The theory of this is well discussed by Faris (Trans.Soc.
Rheology 12:2, pp. 281-301, 1968).

As an example, the Faris study gives an optimal particle size distribution for a 75 wt% coal/water slurry with a particle size of 200 microns, assuming a packing density of 1.2, as shown in the following table.

Table 1 Coal weight % Particle size (μm) 100 −200 92 −160 79 −100 70 −70 59 −44 42 −20 29 −10 In the production of slurry, a predetermined unit volume of slurry is highly filled with solid particles. It is generally a challenge to achieve a particle size distribution that makes it possible to Even if the actual objective is not to obtain a slurry with a very high solids content, it is preferred to use solid particles with a particle size distribution that gives a high solids content. This is because this type of slurry exhibits more favorable rheological properties than slurries containing particles with a poor size distribution at any slurry liquid content.

The published Faris paper shows that there are particle size distributions that give higher solids content than other distributions at a given maximum particle size in a slurry solid. Generally, the ideal distribution will include a greater amount of fine and coarse material within the distribution than is typically produced in a single milling step. Open milling circuits, i.e., milling circuits without internal or external classification operations, produce on average a finer material than closed milling operations when producing products of the same maximum particle size; , this both produces a distribution that tends to heavily concentrate the product in the intermediate particle size range, ie a narrow distribution.

However, the present invention provides a method to achieve the desired particle size distribution at a predetermined maximum particle size in a continuous manner by carrying out the following steps: 1. introducing the crushed carbonaceous starting material into a first mill where it is systematically milled to a coarser particle size distribution than the desired slurry particle size distribution; 2 the milled product from the first mill is subsequently passed through a classifier; to remove rough parts. such that the coarsest particles of the fine fraction are coarser than or equal to the average particle size of the final slurry, but less than or equal to the maximum particle size of the finest slurry, preferably approximately equal to the maximum particle size of the final slurry. It is preferable to choose a cutting point; 3. The coarse part is subsequently introduced into one or more subsequent mills. In that mill, the milling energy per unit of filler material can be varied from the milling energy per unit of filler material of the first mill. Therefore, whatever particle size distribution is required for the product from each subsequent mill, i.e. the fines separated from each mill, and the fines separated from the first mill: The coarse portion can be milled to approximate the ideal or desired particle size distribution.

These steps can be carried out in several milling stages, each milling stage consisting of at least one mill and an optional classifier, except for the first milling stage which requires the use of a classifier. Preferably,
There are a total of two milling stages. For the final milling stage, one can choose to use the classifier from the previous milling stage or not to use a classifier at all. 1st
The separated fine part, which is combined with the fines from the milling stage to form a slurry solid, is of a particle size distribution such that its maximum particle size is less than or equal to the maximum particle size in the slurry. In, the first
Preferably, a classifier is selected for each milling stage following the milling stage. The maximum diameter and average particle size of the fines from the next milling stage that are made into a slurry together with the fines separated in the first milling stage are the maximum and average particle diameters of the fines separated in the first milling stage. than the average particle size,
Preferably, the maximum and average particle sizes are equal or smaller, respectively.

Therefore, the requirement for a sufficiently coarse material in the final slurry can be met especially in the first milling stage, or
The coarse material separated in the first milling stage contributes in particular to the formation of a finer particle fraction by the subsequent milling operation. This allows the operator to continuously achieve the desired particle size distribution, regardless of the tendency of each individual milling operation to form an undesirable particle size distribution.

Other advantages may be obtained by choosing a mill or mills of higher capacity than would be required under normal operation. Additionally, this overcomes operational obstacles that cause the first milling operation to produce a coarser product than expected by increasing the milling work performed in the subsequent milling operation. This makes it possible. As a result, the particle size distribution of the blended fine powder can be maintained around a constant level, and the properties of the slurry can always be maintained almost constant.

It is therefore an object of the present invention to provide a method for producing a slurry of pulverized carbonaceous material having a predetermined particle size distribution consisting of a predetermined average particle size and a predetermined maximum particle size. The method includes a grinding step comprising at least two grinding stages and mixing the ground material with a carrier liquid to form a slurry, the method comprising: (a) grinding the carbonaceous material in a first grinding stage; (b) grinding the milled product from step (a) into a coarse material having an average particle size at least greater than the average particle size of the given particle size distribution and an average particle size smaller than the average particle size of the coarse material; (c) the coarse material from step (b) is further divided into at least one
(d) blending the fine materials from the different stages; and (d) blending the fine materials from the different stages. It is characterized by generating slurry.

This and other objects and advantages of the invention will become more apparent from the following description based on the drawings, in which FIGS. 1 and 2 further illustrate Example 1, respectively.
Two specific examples of the method of the present invention described in 2 and 2 are shown below.

Flexibility given to the operator in controlling the amount of grinding performed at each milling stage and achieving the desired particle size distribution by selecting the cut point in the classification operation to achieve favorable packing conditions in the final slurry It is no less important than what you do. Many factors often need to be weighted together to determine the best distribution. The following are the main factors that can be considered.

- Maximum particle size in the slurry. This is usually determined by the intended end use of the slurry, ie, the maximum particle size that is sufficient to burn out in a particular combustion installation.

− beneficiation properties of the carbonaceous material used; It is often desirable to remove inorganic components from the carbonaceous starting material before forming the slurry. The more finely a substance is crushed, the more inorganic substances will be liberated. Therefore, by lowering the maximum particle size or reducing the amount of coarse material, the operator can improve the removal of impurities in the separation process prior to creating the slurry.

− Milling costs. The finer the average particle size of the slurry, the more costly the milling process.

− effective surface area of the milling product; The final slurry composition often includes chemical additives to enhance the properties and stability of the slurry stream. Additives of this type often include surfactants, so a large effective surface area results in increased additive concentration.

Taking into account the above factors and the desire to obtain a particle size distribution that gives high slurry particle packing, the operator can choose a target particle size distribution and produce it using the mill and classifier described above. . Typically the maximum particle size range is 50-500 microns, preferably 50-250 microns. 1st
50-95% of the material from the mill is at or below this maximum size, and 5-50% of the particles exceeding the selected maximum size are separated in the classification step of the first milling stage, and The separated particles are ground in one or more subsequent grinding stages to an average particle size equal to or preferably smaller than the average particle size of the fines separated in the grinding stage.
Preferably, the first milling stage produces 60-85% of the particles of sufficient fineness contained in the slurry.

However, in applications such as combustion of a fuel slurry in a fluidized bed or injection of a fuel slurry into a blast furnace, the particle size of the pulverized carbonaceous material is not particularly critical and even if the fuel slurry contains relatively large particles. No problems arise. However, if the particles are too large there is a risk of particle settling, so the particle size should be approximately 0.5
Should not exceed mm.

Example 1 In this example a mill apparatus according to FIG. 1 of the attached drawings is used. Mill equipment is 1 at each stage
It includes two milling stages with several wet ball mills. More particularly, the first milling stage consists of a first mill 1 and a sieve bend 2, and the second milling stage consists of a second mill 3 and a sieve bend 4.

The mesh size of the sieve bends is chosen such that sieve bend 2 separates material coarser than the maximum allowable slurry particle size and sieve bend 4 separates into coarse or fine particles which are fed back to mill 3. The material flow is as follows: Carbonaceous starting material (A) and sufficient water are introduced into the first mill; the milled product (B) having 5-50% coarser material than the final slurry solids is passed through the mill. Out; 5-50% coarse material (C) is separated in sieve bend 2 and ground in second mill 3; milled product (D) from second mill 3 is sent to second sieve bend 4 where it is The fines fraction (E) is separated and combined with the fines from sieve bend 2 to produce the final milled product (F); the crude product (G) from sieve bend 4 is passed to the second mill 3
(F) is combined with the slurry liquid to form a slurry product.

Example 2 A high volatility bituminous coal (eg, Cape Breton Development Corporation, Nova Scotia, Harbor Seam coal) was used to produce an aqueous slurry. The maximum slurry particle size selected is
200 microns, and the slurry loading was selected to be 75% by weight. The ideal Furis distribution required the following distribution.

Table 2 Particle weight % Particle size (μm) 100 −200 85.5 −125 76.5 −88 67.0 −63 59.5 −45 51.0 −31.5 42.0 −20 32.5 −12.5 Coal was ground in a wet ball mill, and coarse particles were removed using a hydrocyclone. When separated and fed back to the same mill for milling, the following distribution was obtained.

Table 3 Particle weight % Particle diameter (μm) 100 −200 99 −125 94 −88 86 −63 75 −45 61 −31.5 43.5 −20 29 −12.5 The distribution thus achieved was unsatisfactory. . Also in conclusion, the ideal Furis distribution consumes excess additives in fuel production. Therefore, there are fewer particles with slightly finer diameters than those shown as desirable in Table 2, and
It was determined that 75% loading would produce a particle size distribution with a sufficient amount of large particle size to obtain a slurry with sufficient flow properties. To achieve this, a milling device according to FIG. 2 was used. The milling apparatus according to FIG. 2 includes two milling stages, with one wet mill in each stage and no separate classifier in the final milling stage.

In the configuration shown in FIG. 2, the slurry maximum particle size,
The mesh diameter of sieve bend 3 was chosen to separate particles larger than 200 microns and further mill them in a second milling stage. The capacity of sieve bend 3 was sufficient to effectively separate the coarse material from the milling products of both stages of milling.

The material flow is as follows: carbonaceous starting material (A) containing sufficient water to approximately 50% by weight and having a particle size of 30.8 mm (30.8 mm) or less (1.5 inches or less);
was fed to the ball mill 1 in the first milling stage. 1st
The product from mill 1 (B) is 200 μm throughout the run.
It contained 30-35% of material exceeding 30%, which was separated in a sieve bend and fed to the ball mill 2 for the second milling stage. Here, the diameter further decreased, and then (D) was transferred to the first stage sieve bend, where it merged and became a fine powder stream (E). This gave the following diameter distribution.

Table 4 Particle weight % Particle size (μm) 100 −200 90.5 −125 81.0 −88 70.0 −63 59.5 −45 49.0 −31.5 33.0 −20 21.5 −12.5 The slurry prepared from the milled product (E) was 75
It had a solids concentration of % by weight and exhibited satisfactory rheological properties.

After carrying out the above grinding method, the fine powder portions from the multiple grinding stages are combined and mixed with a carrier liquid of choice to form a finely ground carbonaceous material with or without flow-enhancing chemical additives. Generate slurry.

However, in some cases it is preferable to carry out a beneficiation step in order to remove from the ground carbonaceous material the inorganic impurities that are entrained in the starting material and liberated therefrom during the grinding step. Particularly if the slurry to be produced is aqueous, it is appropriate to carry out the grinding step in a wet mill followed by a wet beneficiation treatment. In such cases, the slurry produced in the grinding process has a solids concentration of 50
From ~25% by weight, it is suitably diluted to typically 5 to 20% by weight, preferably 7 to 15% by weight in a flotation cell device that separates organic particles from inorganic particles.

Here, a sufficient holding time of usually 15 to 45 minutes is provided depending on the concentration and particle size of the solids.

Usually, the flotation process is carried out in a coarse beneficiation series in a flotation cell followed by a refining beneficiation series, where reagents,
For example, flotation agents, accelerators, and depressants can be added independently to each cell of each series.

The carbonaceous pulverized material thus beneficiated is dehydrated to 35-15% by weight by sedimentation and/or filtration techniques, and the dehydrated slurry is used as is or mixed with chemical additives to improve fluidity. Then pump to storage.

If a non-aqueous slurry is to be produced, a dehydration step is suitably used to achieve an even lower water content before the slurry liquid is combined with the beneficent finely divided carbonaceous material in a mixing step.

In conclusion, from the foregoing, the present invention provides a novel method for producing a slurry of finely ground carbonaceous material, including a grinding stage, an optional beneficiation stage carried out in a dilute aqueous phase, and a slurry mixing stage, as well as a method for producing a slurry of finely ground carbonaceous material. It is clear that novel methods of carrying out the grinding step to produce a slurry are provided, both having the features and advantages listed above.

Obvious modifications and equivalents will be apparent to those skilled in the art, and the present invention does not rely on the precise details of operation, composition, method, or composition shown or described above.
Rather than being limited to operation or specific examples, the invention is therefore to be construed as limited only by the full scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a flow sheet diagram of an apparatus for implementing Example 1 of the slurry manufacturing method according to the present invention; FIG. 2 is a flow sheet diagram of an apparatus for implementing Example 2 of the slurry manufacturing method according to the present invention. be. Figure 1, 1...1st mill, 2...sieve bend, 3
... second mill, 4... sieve bend, A... carbonaceous starting material, B... material coarser than final slurry solids, 5...
-50% milled product, C...5-50% coarse material, D...milled product from second mill, E...fine fraction, F...final milled product, G...crude from sieve bend. Product, FIG. 2, 1...first mill, 2...second mill, ball mill, 3...sieve bend, A...carbonaceous starting material, B...product from first mill, C...second
Feed to the mill, D... milled product from the second mill, E... fines.

Claims (1)

[Scope of Claims] 1. A method for producing a slurry of pulverized carbonaceous material having a predetermined particle size distribution consisting of a predetermined average particle size and a predetermined maximum particle size, comprising at least two mills each having at least one mill. A process for making a chiller comprising a grinding step comprising a step of grinding and mixing the ground material with a carrier liquid, comprising: (a) grinding the carbonaceous material in a first grinding step; (b) ) dividing the milling product from step (a) into a coarse material having an average particle size larger than the average particle size of the predetermined particle size distribution and a fine material having a particle size smaller than the average particle size of the coarse material; (c) further grinding the coarse material from step (b) in at least one further milling stage to at least one further milling stage;
(d) mixing the fines from the different stages to form a slurry; and (d) mixing the fines from the different stages to form a slurry. A method for producing a slurry of finely ground carbonaceous material. 2. Process according to claim 1, characterized in that the milling product from the last milling stage is divided into coarse and fine material. 3. Process according to claim 1, characterized in that, except for the last milling stage, all of the coarse material from the different milling stages is milled in the next milling stage. 4. Only a portion of the coarse material from different milling stages except the last milling stage is milled in the next milling stage, while repeatedly milling in the same milling stage or in a preceding milling stage. Claim 1 characterized in that the remaining coarse material is fed back.
The method described in section. 5. Process according to claim 2, characterized in that the coarse material from the last milling stage is fed back for repeated milling in the same milling stage or in a previous milling stage. 6. Claim 1, characterized in that the coarse material from the first milling stage has a particle size of 50 to 500 μm.
The method described in section. 7. Claim 6, characterized in that the coarse material from the first milling stage has a particle size of 50 to 250 μm.
The method described in section. 8. Process according to claim 1, characterized in that the coarse material from the first milling stage comprises from 5 to 50% by weight of the total amount of material entering the first milling stage. 9. Process according to claim 1, characterized in that the particle size of the coarse material to be separated in the first milling stage is at least larger than the maximum particle size of the predetermined particle size distribution. 10. A slurry of pulverized carbonaceous material produced by the slurry production method according to claim 1.